As US climatologists and scientists are urging the world that greenhouse gas emissions be curbed rapidly to prevent runaway global warming, the UK Met Office appears to be back pedalling on human induced climate change. Peter Bunyard reports on some mixed messages

How strange the UK Met Office’s recent back-peddling on human-induced climate change, just at a time when prestigious climatologists and scientists from the United States are telling the world, and not least leaders such as Gordon Brown, that we have very little time left to curb our emissions of greenhouse gases if we want to prevent runaway global warming, with consequences far more severe within the century that even hinted at in the 2007 Fourth Assessment Report of the IPCC — the Intergovernmental Panel on Climate Change.

In warning us that some scientists, unnamed, and, in turn, some journalists are spreading unnecessary gloom and doom by jumping to dramatic conclusions concerning the rate at which we are plunging into the impacts of human-induced climate change, could it be that the Met Office is somehow providing support for the government in its plans to allow new coal-fired plant to be built and, not least, the construction of the third runway at Heathrow? In other words, in these times of a collapsing economy, we must do all in our power to keep the show on the road?

In fact, as reported in The Guardian (Wednesday, February 11th, 2009) no less a person than the head of climate change advice at the Met Office, Dr Vicky Pope, made an extraordinary statement in which she called on scientists and journalists to stop misleading the public with “claim and counter-claim”. She went on to say: “Having to rein in extraordinary claims that the latest extreme event is all due to climate change is at best hugely frustrating and at worse enormously distracting. Overplaying natural variations in the weather as climate change is just as much a distortion of science as underplaying them to claim that climate change has stopped or is not happening.”

Who was she getting at? James Hansen, director of NASA’s Goddard Space Research Institute in New York, who had the courage to challenge the Bush Administration in its denial of human-induced climate change and who has persistently warned us that we are now at the edge when tipping points, such as the melting of Greenland’s ice sheet, could well come into play and cause climate chaos? Or was it Chris Field of Stanford University and the Carnegie Institution for Science, who co-chaired the IPCC in 2007 when it won the Nobel Peace Prize? He has now become outspoken about the dangers we face from a ‘business-as-usual’ emissions scenario. “Higher temperatures,” he says, “could ignite tropical forests and melt the Arctic tundra, releasing billions of tons of greenhouse gas that could raise global temperatures even more—a vicious cycle that could spiral out of control by the end of the century. We don't want to cross a critical threshold where this massive release of carbon starts to run on autopilot.”

But before we listen to Hansen, Field and their ilk, and jump prematurely to conclusions, hadn’t we better make sure first that climate change is no more than the expression of the swings and roundabouts of natural climatic variability? “A common misrepresentation,” Dr Peter Stott, a climate researcher at the Met Office, tells us, “is to take a few years data and extrapolate to what would happen if it continues. You just can't do that. You have to look at the long-term trend and then at the natural variability on top. Dramatic predictions of accelerating temperature rise and sea ice decline, based on a few readings, could backfire when natural variability swings the other way and the trends seem to reverse. It just confuses people.”

What Stott didn’t tell us, is the length of time it takes before scientists are satisfied that climate change trends have been teased out from natural variability. The usual practice is to look back at records over the previous 30 years before drawing definitive conclusions. And what about tipping points, how do they fit into the picture? Do we just smooth out a sudden jump in the records, only to find later, maybe a decade later, that, because of scientific uncertainty, we’ve slid even further down the slope of irreversible climate change?

Well, having been clear in my mind that such prestigious climatologists as James Hansen of NASA were right on the ball in alerting us to a much more rapid melting of Greenland’s ice than had been predicted in the somewhat conservative climate models, referred to by the IPCC, and that Arctic Sea Ice had shrunk to its smallest area recorded during the summer months in 2007, I do indeed find the latest intervention of the Met Office, somewhat confusing.

Do Peter Stott and Vicky Pope honestly think that the accelerating melting of the glaciers in tropical high Andes is likely to be nothing more than natural variability. A decade ago, the Colombian meteorological service (IDEAM) estimated that the glaciers of Colombia’s 20,000 feet plus mountains would take 300 or so years to vanish. Today, Colombia’s Met Office is talking in terms of total loss in a couple of decades, with devastating consequences for the rivers of that country and its fresh water supply. Global warming, averaging at about 2°C over Colombia is certainly doing the trick, at least in good measure, to my way of thinking. Add to that the appalling deforestation which has taken place in the Andean region (less so in Colombia’s Amazon) over the past 50 years and which will have led to dramatic changes in atmospheric humidity and whilst working in Colombia seeing the hand of Man absolutely implicated in Colombia’s loss of glaciers.

And who can tell me that the 2005 unprecedented drought in Amazonia, when rivers dried up and fish in their millions died, was just a one-off event during the course of natural variability? That the drought, which also coincided with the worst ever recorded hurricane season, capped by hurricane Katrina, was not telling us something? If there ever was a climate canary then what happened over the tropical Americas in 2005 should be making us feel a little apprehensive if not downright scared.

To give it credit, the UK Met Office, in the guise of its Hadley Centre for the Prediction of Climate Change, has largely been in the forefront of warnings about climate change and the consequences of global warming from emissions of greenhouse gases. In that respect, climatologists, such as Richard Betts, Peter Cox and a host of others, were among the first worldwide to introduce a dynamic carbon cycle into their general circulation models (GCMs), their aim being to get a handle on how vegetation might respond to global warming, given what we know about the physiology of plants and soils.

What they found was alarming in the extreme. Instead of vegetation, particularly in the tropics and the warmer parts of the planet, benefiting from the fertilisation effect of more CO2 in the atmosphere, ‘business-as-usual’ greenhouse gas emissions resulted in a sharp fall in vegetation’s ability to grow and put on biomass because of the associated sharp rise in temperature, combined with dramatic changes in rainfall. Nor did it end there, the Hadley Centre models showed vegetation die-back and decomposition, including increased vulnerability to fire, with the subsequent release of massive quantities of CO2, methane and nitrous oxide.

Because of the emissions from decaying biomass and increased soil respiration, the Amazon Basin was found to be a major contributor in the jacking up of surface temperatures, which overall rose by half as much again than those predicted in the recent Fourth Assessment Report (2007) of the IPCC. If we were to trust in the Hadley models then surface temperatures over the planet’s land mass could rise by as much as a deadly 9°C on average compared to pre-industrial times.

Of course, there is a world of difference in the predictions generated in climate models and the interpretation of current events. What the models cannot do is to predict a specific extreme weather event; instead they can predict the likelihood of such an event at some place and some time in the future. And not all models agree. That uncertainty could be catastrophic if it leads to a ‘wait and see’ approach and consequent inaction. Do we really have to wait 30 years to tease out natural variability from the consequences of our desecration of essential ecosystems before we can say with some certainty that humans did or didn’t cause some particular aspect of climate change?

James Hansen is one of any number of scientists who sees the abyss of climate change edging ever closer. “The climate is nearing tipping points,” he said (The Observer, Sunday 15th February, 2009). “Changes are beginning to appear and there is a potential for explosive changes, effects that would be irreversible, if we do not rapidly slow fossil-fuel emissions over the next few decades. As Arctic sea ice melts, the darker ocean absorbs more sunlight and speeds melting. As the tundra melts, methane, a strong greenhouse gas, is released, causing more warming. As species are exterminated by shifting climate zones, ecosystems can collapse, destroying more species. Our planet is in peril, with one ecological collapse leading to another. If we do not change course, we'll hand our children a situation that is out of their control.”

Peter Bunyard is the science editor of the Ecologist magazine, and a widely published freelance author and environmentalist. He has worked as consultant editor for the United Nations Environment Programme review on Industry and the Environment, and was secretary and editor of the Committee for the Study of Nuclear Economics. A fellow of the Linnean Society, he has conducted field work in the Colombian Amazon on the role of rainforests in global warming.